No doubt, obesity can be turned into a complex subject. Just look at the diagram below. However, this explanation by Dr. Yoni Freedhoff' sums it up beautifully:

I'd describe obesity as the natural consequence of placing a collection of truly ancient genes, genes forged over millions of years of incredible and constant dietary insecurity and upheaval, into an insane, calorific, modern day, dietary utopia. In other words: Obesity and overweight are our bodies' normal, natural, responses to the world they find themselves living in.

The fact is that right now the accepted global viewpoint is that if obesity is a disease it's a disease of willpower, of gluttony, of sloth.

My hope is that one day obesity will be seen as a modern day scourge, a day when the trite advice "all you need to do is eat less and exercise more" is seen by the general public as over-simplified nonsense.